There has conventionally been known a fiber laser for generating high-power laser light by (i) introducing, into an amplifying optical fiber, excitation light emitted from a laser diode laser light source) and (ii) amplifying laser light in the amplifying optical fiber. Such a fiber laser can generate higher-power laser light by, particularly, (i) combining a plurality of beams of excitation light emitted from a plurality of laser diodes and (ii) introducing the combined excitation light into the amplifying optical fiber. The high-power laser light which has been outputted from such a fiber laser is used in, for example, laser processing or the like.
According to a method disclosed in Patent Literature 1, a fiber laser device including a plurality of laser diodes which emit excitation light controls individual driving currents for the respective plurality of laser diodes. This allows the plurality of laser diodes to be uniform in load (e.g., an electric current flowing in the laser diodes, a temperature of the laser diodes themselves or an ambient temperature of the laser diodes, and the like). With the method, even in a case where the plurality of laser diodes have individual differences in light emission efficiency, calorific value, or the like, it is possible to uniformize lives of the plurality of laser diodes by uniformizing loads on the plurality of laser diodes.
According to a method disclosed in Patent Literature 2, in a multiport optical amplifier including a plurality of excitation light source elements, a driving current for an excitation light, source element which is deteriorated is reduced and a driving current for an excitation light source element which is not deteriorated is increased. This allows the multiport optical amplifier to maintain an intended excitation light power. With the method, it is possible to uniformize lives of the plurality of excitation light source elements as much as possible, so that a usable period of the multiport optical amplifier can be maximally extended.